This invention relates to a bulk material receiver and dispenser with filters wherein a vacuum is drawn in the receiver to induce a flow of bulk material to the receiver, and to a process for back washing the filters of the receiver.
Bulk materials frequently are transported from a source point to a hopper at the use point by means of a vacuum conveying system in which the bulk material is picked up in and moved through a conveying tube extending from the hopper by means of an air stream which is induced through the conveying tube by pulling a vacuum on the hopper. The hopper located at the use or delivery point usually is termed a vacuum receiver or a bulk material receiver. Air which is drawn through the conveying tube with the bulk material must be separated from the bulk material at the receiver so that relatively clean air can pass to the vacuum pump and substantially all of the material transported through the conveying tube drops into the bulk material receiver.
While separation of the material from the air stream presents no significant problems in the cases where the bulk material particles are of sufficient size to readily drop out of the air stream, bulk materials which have fine particles tend to carry over into the air stream exhausted from the receiver and into the vacuum pump, thus presenting a problem in that this amount of material would be wasted if passing through the vacuum pump and the material tends to damage the vacuum pump if not collected prior to passing through the vacuum pump. It is desirable to have a separation or filtration means for separating such fine material from the air stream, and it is further desirable that this filtration means be compact and situated in the bulk material receiver.
Such filtration devices for bulk material receivers have been designed and used in the past; however, with the prior art systems the system for cleaning the filter has presented several problems. One method for cleaning the filter of a bulk material receiver has been to simply allow air from the atmosphere to back flow through the filter when the vacuum pump is stopped at the end of fill cycle of the vacuum receiver. This proves ineffective because the quantity and velocity of air that passes through the filter is low. Another method of back flushing the filter has been the use of compressed air which flushes the filter when the vacuum pump is stopped at the end of the fill cycle. This method can effectively clean the filter; however, the method creates the problem of blowing fine particles out of the bottom of the vacuum receiver, thus creating a health hazard and a cleanliness problem. Similarly, another method used to back flush the filter media has been to reverse the vacuum pump at the end of the fill cycle, thus flushing the filter; however, this creates the same problem of blowing dusty material out the bottom of the vacuum receiver, thus creating a health hazard and a cleanliness problem.
A third method that has been used to back flush filters of a bulk material receiver has been to divert the exhaust of the vacuum pump and use this flow of air to back flush the filter. This method also creates a health and cleanliness problem due to dust flowing from the bottom of the vacuum receiver, and also creates the need for a rather large filter in front of the vacuum pump to handle the substantial carry over to the vacuum pump during the back flushing of the filter.
Another method now in use involves sequentially pulsing compressed air through one of several filter bags contained in the filtration system, thus cleaning one bag while drawing the additional flow generated by the compressed air through the other bags and, hence, to the vacuum pump. This involves expensive compressed air and an expensive sequencing system.